For the generation of X-ray radiation, for example in an X-ray tube, a filament is provided for emitting electrons to impinge on a surface, thereby generating X-ray radiation. In order to provide a focal spot, the exact arrangement of the filament and its positioning is required. Alterations of the filament during operation may lead to a change of the focal spot and thus to a change of the radiated X-ray beam, for example. Therefore, care is taken for a correct positioning of the filament during assembly. For example, during a cathode cup assembly, the required filament shape and also the position of the filament in relation to the cathode head takes place with a predefined accuracy. This is achieved, for example, by manual adjustment. U.S. Pat. No. 6,607,416 B2 describes a fixture for using a mandril to set a filament on an electrode for mounting the filament on a cathode head. However, it has been shown that the securing of the filament ends in the cavities of the cathode may still require final position relating to the direction of the emitted electrons. Further, also the correct alignment of the mounting tool in relation to the cathode cup for properly positioning the filament in the first place has to be carefully observed.